InspectAPedia ^TM

The Nature of Vision - Inspecting Complex Systems, Why We See or Do Not See Things We Are Looking For - Or Should Be Looking For InspectAPedia TM Enter your search terms Submit search form   Search This Website - InspectAPedia.com

• When and Why Inspectors "See" or "Don't See" Things Which are Present
• Inspection methods for any complex system
• Advanced Home Inspector Education

Most people believe that if our eyes are open, we are seeing. Cognitive scientists once thought our visual perception acted much like a videotape recorder. We know now that this is not the case. Perception studies are demonstrating how little people actually see when they are not paying attention.¹. The purpose of this article is to improve the chances that an inspector, charged with the visual examination of any complex system such as a building, its mechanical systems, and its site, will find both the visually apparent and the visually present but more subtle clues which signal important costly repairs, unsafe conditions, or other targets of the inspection. "Inspection" as used here refers to a primarily-visual approach which may make limited use of special equipment such as moisture meters or electrical circuit polarity testers, but which does not involve demolition or similar "invasive" methods to evaluate the condition of a building or similar complex system and its subsystems such as building mechanicals. More in-depth, un-biased, expert information on these topics and on building defect inspection, diagnosis, & repair can be found at "More Information below. © 2007 Daniel Friedman, All Rights Reserved. New York State License # 16000005303

This article is a chapter in the author's "Developing your X-Ray Vision, A Promotion Theory for Forensic Observation of Residential Construction - Levels of Fear, and how to use them to find and report significant, hidden problems." See http://www.inspect-ny.com/vision/vision.htm - The Nature of Vision - inspecting complex systems (this article, online) and see http://www.inspect-ny.com/structure/x-ray.htm for the online version of "Developing your X-Ray Vision." As this is an ongoing study project these articles are updated periodically. Also see http://www.inspect-ny.com/vision/sinkholes.htm about sinkholes in Florida. Also see "The Home Inspection and Construction Information Website" www.inspect-ny.com for free in-depth research on building defect recognition and repair, including both physical defects on buildings and environmental concerns such as mold and allergens.

Surprises in the Study of Vision and Inspection of Buildings or Other Complex Systems

Study in a variety of fields (eye and brain, the psychology of error, the physics of light and optics, microscopy, and aerobiology) has led to some surprises and to recognition that forensic experts and inspectors should not be overconfident in their ability to "see" what they are looking "for." Even the ability to see what we are looking "at" is demonstrated to be incomplete.

Research on Vision Can Inform Inspectors

Several areas of research can inform forensic inspectors and may improve their performance

Neurology and brain function, particularly with respect to "seeing"

Physics and the study of light, particularly optical physics and the detection of objects, both macroscopically (by eye) and microscopically (by instrument)

Psychology of seeing, or "not seeing," the psychology of errors - why we make mistakes or fail to recognize something important, and why we do not, indeed cannot, focus our attention so as to "see" everything that is in our visual field.

I have not attempted to recap everything about these areas, but I will cite a few ideas they suggest and which pertain to the use of an inspection methodology employing techniques to improve recognition of subtle clues of hidden defects.

What is needed in order to "see" any object or object-feature?

Presence: Information or Object Must Be Present

The object or feature must be present in the visual field of the observer so that all the observer needs to do is direct his or her eye there to be [potentially] able to see it. The size and other requisite aspects of the object or feature are discussed below. For purposes of this discussion we refer to normal sighted-human vision, unaided by special equipment such as microscopes or telescopes, though the observer may [indeed should] make use of corrective eyeglasses or contact lenses if their vision has been found in need of those aids. In my longer X-ray Vision article my view is that "clues" which suggest an otherwise "hidden" defect are in fact visual "features" of that very defect or condition and can so can be recognized.

Light: Light Reflects From Object to Eye

Light reflected from a surface towards the eye of an observer carries incomplete information about the object and can be distorted. In any case it will not contain all of even the surface information about the object due to limitations of illumination, optical distortion, and of course the inability to "see around corners." The human eye is sensitive to light (electromagnetic radiation) from around 350 to 750nm in wavelength. It is speculated that we evolved to be sensitive to radiation at these wavelengths because they are so common in sunlight. Some other animals have eyes which are sensitive to electromagnetic radiation at lower wavelengths (such as infra red).

In the process of "inspecting" objects and systems in the field, inspectors use a combination of local natural light, artificial indoor lighting, and flashlights. The flashlight is a more important tool than some inspectors realize. the level or intensity of illumination, angle of illumination, and color of the light source can make the difference between a human's ability to "see" or not see a feature.

The ultimate level of detection of visual features being illuminated by light is a function of the wavelength of the light source, since particles smaller than the wavelength may fail to refract or bend the light waves sufficiently to permit detection. In forensic microscopy the wavelength of the light source is a factor but more important is the ability of the microscope's lens system to direct light rays at the particle being examined. The particle refracts, or "bends" light rays, producing a visible image which is focused by the lens system.

Eye: Light Reaches Eye

The eye, the cornea and lens of the eye itself is the image-forming system for human inspectors working without a microscope or binoculars. The image of the observed object is formed at the back of the eye on the retina where special cells in turn fire neurons which pass the visual image map to the visual cortex of the brain. The human eye can resolve particles down to a few hundredths of an inch or so in diameter.

Brain: Brain Interprets Information

The brain plays a considerable additional role in "seeing" beyond mere image mapping. Additional image data processing occurs in the brain in order to recognize what is being observed.

What a human "sees" is a representation of the objective world built-up in the brain from a combination of sensory inputs and significant additional processing in the brain. While I'm taking some literary license to say so, it would appear most likely that the brain constructs the "image" in the observer's consciousness from a combination of visual inputs from the eye, a map of the eye's input in the visual cortex, and processing of that data along with stored maps of "expected images." As human brains are designed to "make sense" of various sensory inputs, we may do so even if "making sense" means "making it up." Thus our observations are vulnerable to illusion.

Inattentional Blindness: Observer (Home Inspector) Must Pay Conscious Attention s

In addition to the need for an object to be observed, a light source, the observer's eye and brain to form an image, vision also requires a level of attention by the observer. The eye and brain are not a video camera faithfully recording all visual data towards which aimed.

The inspector may fail to see objects even when they are present and readily apparent in the center of the visual field. Perhaps less difficult to grasp is research about forms of blindness or an inability to "see" - change blindness and inattentional blindness in particular. In the forming conscious visual information in the brain, inattentional blindness refers to an observer's blindness to the presence of an object right in the visual field, even though the observer is awake and directing her eyes directly towards it.

Because "seeing" at a conscious level requires both the processing of visual signals from the eye and a processing of the input by the brain to form an "image," research has demonstrated that conscious "attention" is absolutely required to "see" anything. In other words, a person can be "looking" right at something, but if his attention is not focused there as well, he will not see it. Perhaps not at all. [1] The observer is likely to fail to see something significant, even in the center of the visual field, if s/he is not looking for that particular thing - if it's not in the observer's "attention set."

Inspector learn quickly the importance of a comprehensive visual scan of everything. An inspector won't "inspect" a room by only looking at one wall. But now we understand that merely directing the eyes at every surface may be quite insufficient.

What's tricky about this is that the inspector believes s/he has "looked-at" a surface, but may not have "attended" to it.

Change Blindness

Researchers in this area describes "change blindness" - the inability to "see" a component change between two rapid presentations of an image, and "inattention blindness [IB]which describes an inability to register and use visual information if attention is not properly focused. "Inattention blindness" is most pertinent to inspectors and recalls earlier work on the psychology of errors, and capture errors.

Kristin's Cards: A Demonstration of Inattentional Blindness

The ease with which IB occurs is nicely demonstrated by Kristin's Cards at http://www.cs.bris.ac.uk/~cater/PhD/Magic/cardtrick.html . I will leave the explanation of the viewer's inability to "see" something important to Kristen.

Factors Affecting Inattentional Blindness

"Seeing" involves conscious mental effort and focus, a task from which observers can be distracted or which can fail due to IB. Four factors affect inattentional blindness: conspicuity [both sensory and cognitive], mental workload [too much or too little], expectation [attention set], and capacity. [Reference 5]

An inspector is more likely to see what s/he is looking for, and outside of that set, to see that which is familiar or large.

Home inspectors are not "seeing" everything that is present, even when it's right in the center of their field of view.

An inspector is less likely to see something that s/he is not expecting, even if it is important and visually distinct by characteristics such as shape, color, or motion.

An inspector's "attention set" of expectations filters out other stimuli. An inspector is less likely to "see" a defect in a structure or system being examined if s/he does not already have an in-depth and visceral understanding of the construction and operation of the structure or system, leading to a broad and deep "attention set."

Eye and Brain, the Psychology of Seeing, Richard L. Gregory, 5^th Ed, Princeton University Press 1997, ISBN 0-691-04837-1 (See Ch. 8, "Learning how to see")

More Information on Building Diagnostic Inspections and Repairs

...

InspectAPedia ^TM Home & Site Map - Building Inspection, Diagnosis, & Repair, Environmental Inspection & Testing - Research Website

The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

Home Inspection Construction Consulting Services & advice for home buyers

Contact Daniel Friedman for website content suggestions or for fee-paid consulting

	Enter your search termsSubmit search form
	Search This Website - InspectAPedia.com